Hydraulic fluid systems are utilized to generate power in a variety of industries. Mining and drilling equipment, construction equipment, motor vehicle transmission systems, and various other industrial applications employ such hydraulic systems. In hydraulic driving or control, a hydraulic pump pumps hydraulic fluid to a hydraulic motor with an output shaft that drives rotation of an end use element (e.g., wheel axle, gear box, rotating fan, or other suitable usage). The motor output that drives the output shaft is regulated through the control of hydraulic fluid flow through the system.
One type of hydraulic motor is commonly referred to as a gerotor motor. In a basic configuration of a hydraulic gerotor motor, a rotating element or rotor rotates relative to an outer element or stator. Surface features on the diameter surfaces of the rotor relative to the stator create variable displacement windows or pockets for the entry and exit of hydraulic fluid that is pumped through the motor via the action of a hydraulic fluid pump. Pressure differentials among the windows or pockets cause the rotor to rotate relative to the stator, and such rotation in turn drives the rotation of an output shaft. The control of fluid flow into the motor pockets is controlled by porting in a commutator or timing valve. Positioning of the commutator or timing valve causes the porting to supply different motor pockets with hydraulic fluid in a progressive manner around the periphery of the rotor in such a way as to maintain pressure in the correct pockets to maintain further motion of the rotor.
One conventional type of hydraulic gerotor motor is commonly referred to as a Ross motor (named for its principal inventor). In a Ross motor, the rotor is provided with a plurality of lobes that rotate relative to a plurality of vanes provided in the stator. In an exemplary configuration, the rotor has six lobes that rotate to mesh and interact with seven vanes on the stator. For the lobes of the rotor to effectively mesh with the vanes of the stator, the stator is essentially fixed and the rotor rotates eccentrically, meaning that the rotor orbits within the stator as well as rotates. However, the orbiting movement of the rotor must be converted to a pure rotation of the output shaft so as to provide a smooth driving of the output shaft. To accomplish this pure rotational output, a drive link is provided that effects a link between the rotor and the output shaft. The drive link operates to convert the orbiting of the rotor to a pure rotation of the output shaft. The addition of a drive link, however, has a drawback in that such additional component is required for the motor, which increases cost and size, and provides another potential point of maintenance or failure of the motor. Furthermore, the stator tends to be more difficult to machine than the rotor, so having the vanes on the stator presents a relatively large complex and expensive manufacturing process.
In a conventional Ross motor, a timing valve is provided for precise timing of the flow into and out from the motor pockets. The flow paths through the timing valve tend to be spiraled so as to provide the precise timing in a minimal amount of space. The spiral flow paths, however, also may be restrictive creating flow losses and potentially limiting the size of the motor pockets. In a variation on the basic Ross motor, still having the vanes on the stator and lobes on the rotor, a timing valve is provided at the end of a second drive link. As referenced above, a first drive link converts the orbiting movement of the rotor to a pure rotation of the output shaft. In the variation, a second drive link ensures pure rotation of the timing valve for proper timing of flow into and out from the motor pockets. The valve system variation from the conventional Ross motor configuration permits the use of essentially straight ports through the timing valve, which in turn permits relatively large motor windows or pockets. This increases the power potential for a given flow rate of hydraulic fluid as compared to a conventional Ross motor. The use of a second drive link, however, further increases size which can be unsuitable for certain applications, and constitutes an additional potential point of maintenance or failure of the motor.
Another conventional type of hydraulic gerotor motor is commonly referred to as a Nichols motor (also named for its principal inventor). In a Nichols motor, the configuration of the vanes and lobes is basically reversed as compared to a Ross motor. The Nichols rotor is provided with a plurality of vanes that rotate relative to a plurality of lobes provided in the stator. In a Nichols motor, the rotor only rotates in a pure fashion, without any orbiting motion. To maximize the mesh interaction of the vanes and lobes, the stator in the Nichols motor orbits within an outer housing. Because the rotor only rotates, the rotor's motion may be imparted directly to the output shaft, thereby eliminating the need for the additional component of the drive link. By providing the vanes on the rotor, machining the stator is more efficiently accomplished as compared to the Ross motor. In addition, by avoiding the drive link a size reduction is accomplished, although Nichols motors tend to have a larger diameter due to the additional housing in which the stator orbits.
A conventional Nichols motor has a timing system comparable to that of a conventional Ross motor. In this manner, the second drive link of the alternative timing valve configuration likewise is avoided to reduce overall size. The Nichols motor, however, has a drawback in that the vanes-rotor/lobes-stator configuration, combined with the orbiting stator, reduces the potential window or pocket size for a given size motor as compared to a motor with a drive link driven timing valve. To achieve comparable power as a similarly sized motor with a Ross lobe/vane configuration combined with a drive link driven timing valve, the flow rate of hydraulic fluid in the Nichols motor must be increased, which in turn increases undesirable flow losses.
Conventional motor configurations, therefore, have drawbacks. A user, for example, must balance the larger pockets but the need for multiple additional drive links against the elimination of the drive links but the higher flow rate and losses of the Nichols motor. The need to choose between associated advantages and deficiencies of conventional hydraulic motors is undesirable.